The invention disclosed herein is generally related to drills and socket drive tools used for forming holes in sheet metal articles. More particularly, the present invention is related to drive tools for sheet metal draw punches.
Electricians must frequently form holes of various shapes and sizes in sheet metal control boxes, cabinets and panels. Such holes are used for routing electrical conduit, as well as for mounting control switches, indicator lamps and the like. Such holes typically range in size from one-half to two inches in size. The holes are typically formed using draw punches, which are also known in the trade as knock-outs. A draw punch typically includes a female die which receives a male punch. The female die includes a central opening through which is extended a threaded draw shaft, or bolt. The draw shaft is engaged in a central threaded bore in the male punch.
In practice, a pilot hole is first formed in a metal panel at the center of the desired hole location. The pilot hole is sized to receive the draw shaft of a small draw punch. The draw shaft is passed through the female die and thence through pilot hole to be engaged with the male punch on the opposite side of the metal panel. When the draw shaft is tightened, the male punch is drawn into the female die, punching a slug out of the panel. The draw punch is typically driven using a manually driven ratchet drive tool or a hydraulically actuated drive tool.
A single draw punch is used as described above for forming small holes, on the order of one inch or less in diameter. If a larger hole is desired, a two-step punching operation is required, with a small draw punch being used as described above to form a pilot hole for the draw shaft of the larger punch. This two-step operation is required because the larger punches have draw shafts which are normally so large in diameter that it is impractical to form a pilot hole in the ordinary manner with a simple drill.
Thus, the forming of a two-inch hole in a metal panel requires three operations with three separate tools, namely a pilot drilling step using a conventional electric drill and pilot drill bit, and two punching steps. The latter punching steps each require the assembly and disassembly of a draw punch. The overall operation is thus time consuming, particularly because of the assembly and disassembly of the draw punches, and because of the manual driving of the draw punches.
Accordingly, it is an object and purpose of the present invention to provide a combination tool assembly which functions as both a drill unit for forming a pilot hole and as a drive tool for subsequent punching steps using one or more conventional draw punches.